Conventionally, the navigation apparatus and other vehicular apparatuses use hard disk drive for storing map data, application programs and the like, and those apparatus access the hard disk drive for reading data therefrom. This is because the hard disk drive is convenient for storing a large volume of data, and, due to the variety of apparatuses used in the vehicle, not only the map data, but also music data, image data, movie data and the like can be conveniently stored in the hard disk drive for quick and easy retrieval.
The hard disk drive uses a magnetic head for reading and writing information on a disk shape storage medium that has a layer of magnetic material applied thereon. At the time of operation of the hard disk drive, the magnetic head located above a disk is raised therefrom by a pressure of air induced by the rotating disk by a small amount of distance. Therefore, a gap between the magnetic head and the rotating disk cannot be maintained in an appropriate condition due to a decrease of the air pressure for raising the magnetic head if the hard disk drive is operated in an environment where atmospheric pressure is extremely low. As a result, the magnetic head collides with the rotating disk to cause breakage of the disk. In other words, the hard disk drive has a restriction in terms of operational altitude due to the decrease of the atmospheric pressure in proportion to altitude increase. In general, the operation of the hard disk drive is guaranteed at an altitude of up to 3,000 meters to 5,000 meters (i.e., an altitude causing atmospheric pressure decrease down to 0.7 to 0.5).
Therefore, when the apparatus having the hard disk drive for use in a vehicle is brought to the high-altitude area that is higher than the operation guaranteed altitude of the hard disk drive, that is, a road at an altitude of 3,000, 4,000 or 5,000 meters, a disk breakage prevention measure is required.
A technique for coping with the problem of the hard disk drive caused by the travel of the vehicle in the high-altitude area is disclosed in, for example, a Japanese patent document JP-A-2004-317385 (U.S. Pat. No. 7,171,305). The technique in the above disclosure stores (i.e., copies) a part of the map data that is originally memorized on the hard disk drive to an external memory prior to stopping the operation of the hard disk drive when the vehicle reaches the high-altitude area at an altitude of a predetermined value or above (e.g., altitude of 3,000 meters or greater), and performs route guidance based on the map data stored in the external memory while the vehicle travels the high-altitude area above the predetermined altitude. The above technique prevents the breakage of the hard disk drive by stopping the hard disk operation in a travel of the high-altitude area, without disturbing continuation of the route guidance.
However, as disclosed in the above document, a large storage capacity must be reserved in a storage medium such as the external memory, because of the size of the map data used in the travel of the vehicle in the high-altitude area. Therefore, the navigation apparatus includes the storage medium having the large storage capacity, only to result in the price increase of the product, or alternatively, excludes the large storage medium to abandon the route guidance function in the high-altitude area during the operation stoppage of the hard disk drive.
As a result, the navigation apparatus loses its trust of the user by discontinuing the route guidance in the high-altitude area due to the non-operation of the hard disk drive leading to the loss of the required map data. That is, the restriction of the navigation function leads to the inconvenience of the user. In other words, avoiding the function restrictions caused by the non-operation of the hard disk drive in the high-altitude area without using the large storage medium has been the long-felt needs of the navigation apparatus and other apparatus using the hard disk drive as the data storage.